Anodic Dissolution Of Tungsten Research Articles

Improved Electrodialysis Synthesis of Perrhenic Acid from the Electrolytes of Processing the Wastes of Tungsten–Rhenium Alloys

The voltage drops across the elements of a three-chamber electrolytic cell are measured during the synthesis of perrhenic acid from potassium perrhenate, and the main contribution to the total bath voltage is shown to be made by the central chamber solution because of the low solubility of potassium perrhenate. The direct electrodialysis recovery of rhenium from the alkaline electrolytes formed during the anodic dissolution of tungsten–rhenium alloys is found to be unreasonable because of a rapid decrease in the process rate and high electric power consumption. The cleaning of tungsten–rhenium electrolytes from tungsten for the subsequent recovery of rhenium from a solution in the form of perrhenic acid is tested. The application of this technological sequence is shown to decrease the electric power consumed for electrodialysis fivefold and to decrease the rhenium losses die to the elimination of the stage of precipitation of potassium perrhenate. A fundamental technological scheme of the process is proposed.

Influence of partial pressure of water vapor on anodic dissolution of tungsten from super hard alloy tools in molten sodium hydroxide

As part of an ongoing study of a new tungsten recycling process using a molten sodium hydroxide bath, in which tungsten is anodically dissolved in the melt from tungsten-containing secondary resources, the influence of the partial pressure of water vapor on the electrochemical behavior of tungsten, cobalt, nickel, and tungsten carbide was investigated. Cyclic voltammograms of cobalt suggested that the solubility of cobalt compounds increased with the partial pressure of water vapor, whereas tungsten and tungsten carbide underwent no significant changes during their oxidation step. In addition, the current attributable to the evolution of hydrogen gas was measured when the partial pressure of water vapor became higher than 0.5atm. On the basis of the abovementioned results, anodic dissolution was carried out at a constant cell voltage using a super hard alloy tool. When water vapor was introduced into the system, the cell voltage and period required to dissolve the entire tip were reduced, even though the applied cell voltage was less than half that required under a pure argon atmosphere. These results indicate that the introduction of water vapor has the potential to improve the anodic dissolution step in the tungsten recycling process using a molten sodium hydroxide bath.

Anodic Dissolution of Tungsten from Super Hard Alloys in Molten Sodium Hydroxide

Anodic dissolution of tungsten in a molten sodium hydroxide bath was investigated at 723K in order to simplify a tungsten dissolution step during tungsten recycling process from secondary resources like used super hard alloy tools. Cyclic voltammetry using tungsten, tungsten carbide and cobalt, which is used as binder in super hard alloys, electrodes suggested that tungsten is easily oxidized and dissolves into the melt. Cobalt was also oxidized and formed oxide or hydroxide film. When water vapor was introduced into the system, the obtained cyclic voltammograms changed with the partial pressure of water vapor. Based on the above mentioned results, anodic dissolution was carried out at constant voltage using throw-away tips as actual secondary resources. When the throw-away tip was anodically oxidized, both the tungsten carbide and binder metal of cobalt were dissolved at constant voltage of 1.0 V, and whole the tips were dissolved by a long-term electrolysis of 20 hours. Although the dissolved tungsten remained in the melt, the greater part of dissolved cobalt deposited as metal powder on the cathode. The current efficiencies of tungsten carbide dissolution were calculated to be 96%. When 0.7 atm of water vapor was introduced, the electrolysis was terminated within 5 hours, which indicates the effectiveness of water vapor pressure control in the present process.

Anodic Dissolution of Tungsten from Super Hard Alloys in Molten Sodium Hydroxide

Anodic dissolution of tungsten in a molten sodium hydroxide bath was investigated at 723K in order to simplify tungsten recycling process from secondary resources like used super hard alloy tools. Cyclic voltammograms suggested that tungsten is easily oxidized and dissolves into the melt. Cobalt, which is used as binder metal, was also oxidized and formed passive film having certain solubility in the melt. When water vapor was introduced into the system, the obtained cyclic voltammograms changed with the partial pressure of water vapor. Based on the above mentioned results, anodic dissolution was carried out at constant cell voltage using throw-away tips as an actual super hard alloy tool. When water vapor was introduced into the system, the cell voltage and duration required to dissolve whole the tips were reduced.

溶融水酸化ナトリウム中におけるタングステンの酸化溶解

溶融水酸化ナトリウム中におけるタングステンの酸化溶解

Electrochemical synthesis, X-ray single crystal, IR spectroscopic, and quantum chemical investigation of molybdenum and tungsten hexamethoxides.

The anodic oxidation of molybdenum metal in MeOH at both low anodic and cathodic current density (0.025 A/cm2) and electrolyte temperatures kept below 20 degrees C provides an efficient approach to Mo(OMe)6 (I). W(OMe)6 (II) can be obtained from the electrolytes, prepared via anodic dissolution of tungsten, by fractional crystallization. The symmetrically independent units in the structures of I and II, being isomorphous, follow the C1 (slightly distorted D2d) symmetry. Theoretical calculations performed for a free molecule of I indicate that this low symmetry may be the result of the packing of the molecules in the crystal structure and also an inherent property imposed by the bonding in this compound. Crystal data for I: Mo(OMe)6 at 22 degrees C, a = 7.0976(13), b = 6.6103(12), and c = 12.286(2) A, beta = 90.068(3) degrees, V = 576.41(18) A3, monoclinic P2/n, Z = 2. Crystal data for II: W(OMe)6 at 22 degrees C, a = 7.1164(19), b = 6.6414(18), and c = 12.304(3) A, beta = 90.047(5) degrees, V = 581.5(3) A3, monoclinic P2/n, Z = 2.

Electrochemical dissolution of tungsten under pulsed conditions

Limiting diffusion currents for the anodic dissolution of a tungsten rotating disc electrode in alkaline solution under rectangular current pulses have been determined experimentally. These currents were calculated by use of approaches developed by Ib1, Cheh, and Chin. Experimental and calculated results were compared. It is shown that the use of bipolar voltage pulses enhanced the anodic dissolution of tungsten in alkaline medium.

Oxide anodes in electro-organic oxidation. Oxidation of maleic addon tungsten oxide anodes

The electrochemical oxidation of maleic acid on tungsten anodes has been investigated. Glyoxal and carbon dioxide were the main products together with tartaric acid and acetaldehyde. Glyoxal is also obtained as the main product from the oxidation ofd-tartaric acid. Under the same conditions succinic acid is completely oxidized to carbon dioxide and water. The anodic dissolution of tungsten and the oxidation of water to oxygen become predominant in the final stages of the electrolyses.

Electrochemical Behaviour of Tungsten: II. Corrosion and anodic dissolution of tungsten in alkaline phosphate solutions

Abstract Open-circuit potential and galvanostatic polarisation measurements were made on tungsten in alkaline phosphate solutions. The rate of anodic dissolution of tungsten strongly depended on pH and showed a Tafel slope of 60 mV/decade. The reaction order with respect to OH− was found to be 1. An increase of temperature at constant pH increased the dissolution rate of tungsten, and the activation energy. ∆H*,for the dissolution process wasfound to be 125 kJ/mol.

The anodic dissolution of tungsten in alkaline solution

The anodic dissolution of tungsten has been investigated over the pH range 9–14. The current-potential curves show a Tafel region followed by a limiting current which is stirring dependent. The results have been interpreted as due to the formation of a WO 3 or hydrated WO 3 layer on the electrode surface which can reversibly dissolve in the electrolyte leading to a dependence of the current on diffusion layer thickness. Impedance measurements show only a charge transfer resistance in parallel with a double layer capacity (with a Warburg impedance additionally present in the region of limiting current).

The anodic dissolution of tungsten ]in alkaline solution

The anodic dissolution of tungsten has been investigated over the pH range 9–14. The current-potential curves show a Tafel region followed by a limiting current which is stirring dependent. The results have been interpreted as due to the formation of a WO3 or hydrated WO3 layer on the electrode surface which can reversibly dissolve in the electrolyte leading to a dependence of the current on diffusion layer thickness. Impedance measurements show only a charge transfer resistance in parallel with a double layer capacity (with a Warburg impedance additionally present in the region of limiting current).

The Anodic Dissolution of Tungsten

The anodic dissolution of tungsten was studied in solutions and solutions at 25°C. Faradaic efficiency studies in basic solutions showed the metal to be oxidized to the +6 state. In acid solutions, a thick protective film of yellow was formed. Polarization curves possessed linear Tafel regions at potentials slightly more positive than the rest potentials. An anodic dissolution mechanism is proposed which involves a surface film of that is further oxidized to and dissolves by hydrolyzation.

The electrochemical behaviour of tungsten—I. The dissolution of tungsten and tungsten oxides in buffer solutions

The anodic dissolution of tungsten in solutions of pH 0·3 to 12 was studied. The current/potential curves consisted of a Tafel region and a plateau and showed no evidence of oxygen evolution. The height of the plateau was found to be proportional to c 0.3 0H − for pH 2·2–8·0, and the open-circuit potential was found to decrease by 43 mV/pH. Pitting was found on polarization at potentials lying in the plateau region for long periods of time. Coloured films are formed on tungsten at cell potentials of 15–1000 V. Studies were also made on electrodes consisting of W powder or one of the oxides WO 2, W 18O 49 or WO 3 plus Plexigum and graphite. Current/potential curves of WO 2 electrodes were found to have the same characteristics as those of solid tungsten, so that the rate-determining step is assumed to lie somewhere between WO 2 and WO 3.